This paper conducts a study on a pre-mixed micro abrasive water jet machining system. A new kind of abrasive mixing tank and the jet system are designed and tapped for the pre-mixed micro abrasive water jet machining system. The performances of the pre-mixed micro AWJ machining system are tested, and some polishing experiments are conducted for hard-brittle materials such as silicon nitride. The results show the feasibility and the advantage of the pre-mixed micro abrasive water jet machining system for polishing hard-brittle materials.